We will continue studies on the nature of the antibodies that constitute a cross-reactive idiotype in an inbred strain of mice. The antibodies investigated are reactive with the p-azophenylarsonate hapten in the A/J strain. Studies of serology and amino acid sequences of hybridoma products show that the antibodies constitute a family of idiotypically related but nonidentical molecules. To further define the cross-reactive idiotype (CRI) we will furnish hybridoma products to Dr. J.D. Capra for additional sequence analyses. Antiidiotypic antibodies will be prepared against individual CRI-positive hybridoma products (HP's) and allowed to react with other labeled CRI-positive HP's; by studies of inhibition of such cross-reactions we will ascertain whether different CRI-positive HP's share at least one invariant idiotypic determinant; and by testing the effect of specific haptens on the idiotypic cross-reaction we will ascertain whether the shared determinants are site-related. Studies will be continued on the nature of an idiotype-specific T-cell derived suppressor factor (TsF) which has antiidiotypic determinants. We will further characterize its molecular properties and compare them with those of a TsF that bears idiotypic determinants. We will also determine whether this factor preferentially induces the proliferation of antiidiotypic suppressor T-cells and whether the antiidiotypic T-cells can induce idiotype-positive suppressors.